The effect of body mass index on the risk of surgical site infection

Abstract

Background/Objectives: Many surgeons believe that obesity puts patients at greater risk of postoperative complications. This review sought to determine whether increased body mass index (BMI) affects the incidence of surgical site infection (SSI) following spinal surgery. Methods: A retrospective chart review was performed for all patients, 19 years to 89 years of age, who underwent spinal surgery at a major teaching hospital during calendar years 2006-2008. Patients (n52121) were categorized as either obese (BMI >530) or non-obese (BMI <30). Variables analyzed in addition to BMI included sex; age; race; type of insurance; Zip Code; ASA Score; diabetes; arthritis; renal failure; coronary artery disease; cancer; smoking history; alcohol usage; site of surgery; surgical approach; Risk Index; emergency; trauma; wound class; surgery not completed within 75{%} surgery cutoff time; prophylactic antibiotic timing; surgeon; SSI; type of SSI; organism causing SSI; and whether or not patient died during the same admission as surgery. The significant variables were identified using Pearson Chi-square or t-test analysis as appropriate. Logistic regression analyses and correlations were performed. Results: From the population of 2121 patients who had spinal surgery during the study period, there were 69 surgical site infections (3.3{%}). Association with SSI was significant for the following variables: 65 years and older (P = 0.040); BMI >= 30 (P = 0.003); diabetes (P = 0.001); cancer (P = 0.001); posterior approach, all sites (P < 0.001); ASA Score (P < 0.001); not within the 75{%} cutoff time for surgery (P = 0.002); and Risk Index (P < 0.001). The final logistic regression (with SSI as the dependent variable) included three independent variables. The logistic regression coefficients were BMI . 5 30 (P = 0.044, odds ratio 1.675, 95{%} CI 1.014 to 2.767); diabetes (P = 0.019, odds ratio 2.017, 95{%} CI 1.125 to 3.617); and not within the 75{%} cutoff time (P = 0.013, odds ratio 1.872, 95{%} CI 1.143 to 3.066). Conclusion: This retrospective review provides support for the belief that obesity is associated with increased risk of SSI. In this population of spinal surgical patients, there was an association between BMI >=30 and surgical site infections, and this association remained significant after controlling for other factors. There was also a multivariate association between SSI and BMI >= 30, diabetes, and surgeries not performed within the 75{%} cutoff time.